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I have 245/70/19.5's on my dually. I looked up all the info on the tires on the net. Under tire calibtation, I can not get these to match the info from the net. If I enter the tire diameter then the circumference doesnt match, same as revolutions per mile. Thats according to the chart on the net. Whats the better of the three numbers to enter. I entered in diameter and so far the speedometer seems alot closer, wont know to I find my gps.
IT is all just math, IF the tread is 245 mm, and the sidewall is 70% of the tread, modified by the 19.5...
The most accurate measurement you can enter isQuote:
Originally Posted by minytrker
"Wheel revolutions per mile" - but that is too difficult to measure without specialized equipment.
The next most accurate measurement is tire circumference. You can measure that by measuring the distance travelled in one complete tire revolution. I recommend using this method. If you can measure the distance travelled in 10 tire revolutions (then divide by 10) that will further reduce any measurement inaccuracies.
The next most accurate measurement is tire diameter. You can measure that from the ground to the top of the tire.
The least accurate "measurement" is using the width/profile/rim values.
P.S. There is a bug in the speedo calculator when entering wheel revs per mile - it incorrectly converts that value between km and miles. An update to fix that bug is being released later today.
Regards
Paul